Microflash tester



Patented July 6, 1954 2,682,765 MIoRoFLAsH TESTER Philip McCutchan, Long Beach, and Dean Arthur Young, Whittier, Calif., assignors to Union Oil Company of California, Los Angeles, Calif., a corporation of California Application July 31, 1951, Serial No. 239,557

Claims.

This invention relates to an apparatus for determining the flash point of inflammable liquids such as petroleum fractions on a micro scale. 4 Y

The flash point of inflammable liquids such as petroleum liquids is a test which is of great practical value, since it serves as an indication of the degree of inflannn ability of the liquid. At present there are three standard methods for determining flash point, namely the Cleveland Open Cup method, the Pensky-Martens method and the Tagliabu Closed Cup method. All of these methods require between 50 and 70 ml. of sample for each test, and where only smaller amounts of sample are available, as is frequently the case, particularly in research work, no method is presently available for determining the flash point.

It is an object of the present invention to supply a method and apparatus for determining the flash point of petroleum products or other inflammable vmaterials on a micro scale, 1. e. by the use of not morethan 1 ml. of sample and in many cases as little as 0.1 ml. or less of sample.

Briefly, the invention involves use of a solid block of highly heat-conductive material, which is adapted to provide a small flash chamber in its central portion, with means for permitting a limited circulation of air from the outside of the block to the flash chamber, and means for heating the block, means'for measuring its temperature at a point adjacent the flash chamber, means for producing the spark in the flash chamber and means for observing the flash in the chamber.

The invention will become more clear by reference to the attached drawing in which Figure 1 is an elevation, partly in section, of an apparatus of the present invention; Figure 2 is a sectional view through the center of the block and perpendicular to theplane of Figure 1; Figure 3 is a sectional view through 33 of Figure 2; and Figure 4 is a schematic diagram of the spark coil circuit employed in the spark coil of Figure 1.

The same numerals are employed to designate corresponding parts in all of the figures. Referring particularly to Figures 1, 2 and 3, block I is a cylindrical block of highly heat-conductive material such as a metal. Shaft 2 is a vertical hole drilled part way through the block near its center, so as to provide, a vapor space 3 above liquid receptacle 4. Just above the liquid receptacle 4, a sloping observation port 5 extends from the flash chamber to the side of the block; and also from just above the liquid receptacle 4 a 2 passage 6 is provided for accommodating the igniter l which contains an electrode 8 which is insulated from the block I except at its inner tip.

The igniter is provided with a flange 9 which,

serves to maintain the electrode 8 in its proper position in the vapor space, and which may also be employed to limit the passage of air through the passage 6. Electrode 8 is connected to one terminal of a spark coil I0, the other terminal of which is grounded or attached to block I. Spark coil i0 is actuated by a source of electric current indicated as volt A. C., which is applied as desired through switch I I.

For heating the block I a burner l2 may be used, surrounded by a shield l3. For measuring the temperature of the block, a thermometer well [4 is drilled so as to terminate adjacent to but separate from the liquid receptacle 4. The thermometer l5 rests in the well It and measures the temperature of the block adjacent to the flash chamber, which is substantially the same temperature as the flash chamber itself, since both the thermometer bulb and the flash cham: ber are centrally located Within the block.

Vertical shaft 2 is at least partially closed at its top by means of cap t6, which has a vent hole 11 passing vertically through its center.

Turning now to Figure 4, this shows the spark coil circuit. It is a conventional vibrator and spark coil in which vibrator 20 is electrically connected to one terminal of the input electric circuit, the other terminal of which is connected to the center of the primary winding 2! of the transformer. The two terminals of the primary winding 2| are connected to contact points adjacent to and on opposite sides of vibrator 20. The two terminals of the secondary winding 22 of the transformer are connected to the output. One of these, the one which is shown connected to block I of Figure l, is grounded. In the operation of the spark coil, 1. e. when switch II is closed, the current flows through one-half of the primary winding 2!, and vibrator 26, which is normally resting against one of the contact points and is situated Within the magnetic field of the transformer, is attracted to the opposite contact. When it leaves its original contact and touches the opposite contact, the current flows through the other half of the primary winding, the magnetic field is reversed, and vibrator .20 is attracted back to the original contact. Each making and breaking of the primary circuit induces a high voltage in the secondary circuit, which discharges through electrode 8 of Figure 1 causing a spark between it and the walls of the vapor space 3.

In the operation of the flash tester, the sample of inflammable liquid which is to be tested for flash point is placed in liquid receptacle 4, as by means of a pipette introduced through observation port or through vertical shaft 2 with cap 16 removed. Cap I6, thermometer l5 and igniter i are placed in their proper positions. Burner I2 is then lighted and adjusted so as to heat the block I at the desired rate, which is determined by periodic inspection of thermometer I5. At appropriate intervals, switch it is momentarily closed so as to cause a spark at the end of electrode 8. The result is observed through observation port 5, and the lowest temperature at which this spark causes an explosion or visible flame at the surface of the sample is noted. This is the flash point.

As indicated previously, there are three difierent flash point tests currently in use, and it is of course desirable that the micro flash tester of the present invention give the same test results for the same sample and the same test, as do the macro testers currently in use. been found that the same block may be employed for all three tests, if certain changes in auxiliary equipment are made. In general the changes involve alterations of the equipment so as to change the degree of circulation of air into the vapor space above the flash chamber, and/or the size of the vapor space.

As a specific example of an apparatus of the present invention suitable for duplicating the Cleveland Open Cup test results, block I is a cylindrical aluminum block 2 inches in diameter and 2 inches long. Vertical shaft 2 is a inch hole drilled to a depth of 1% inches. Vertical thermometer well It is drilled adjacent thereto to a 2-inch depth. 0.3 ml. of sample is to be used in the apparatus, and its surface will lie somewhat less than V inch above the bottom of shaft 2. Observation port 5 is an inch hole drilled at an angle of 20 above the horizontal so that it terminates just above the liquid surface; and passage 6 is a inch horizontal hole drilled to enter the passage 2! about inch above the surface of the sample.

The igniter 7 consists of a platinum wire electrode ii sealed in through 3 mm. outside diameter glass tubing. The electrode 8 is bent downward at its tip and located near the edge of passage 8. This prevents observation of the spark while testing for the flash. The spark coil Ii] is of such size as to produce a spark of an energy of about 1 millijoule. For safety, switch I! is composed of two spring switches, one in each line, located at opposite sides of the equipment, so as to make it substantially impossible for the operator to cause a spark accidentally. Cap l5 has a -inch diameter lower section 7 inch long which fits into passage 2, the upper portion of which is enlarged sufficiently to accommodate it, and an upper section inch in diameter and inch deep. The vent hole ll passes vertically through its center, and is 4,4, inch in diameter. Burner I2 is a small Bunsen burner, and thermometer I5 is a conventional Cleveland Open Cup flash thermometer commercially available.

In determination of the Cleveland Open Cup flash point, the rate of heating of block I is controlled by adjustment of the burner l2 so as to raise the temperature of the block at the rate specified in the standard (macro) method identifled as the ASTM method D92-46 published It has periodically in the Journal of the American Society for Testing Materials. The switch H is closed at the intervals specified for flashing in the standard method, and the flash point is observed as specified in this method.

Results of extensive tests with the above micro tester have shown excellent correlation with results obtained with the conventional Cleveland Open Cup testing apparatus. It has also been found that the micro method is less susceptible to error through variations in rates of heating, and is much more rapid and easy to employ, than is the standard micro method.

In employing the above apparatus of this invention for duplicating the Pensky-Martens flash point, a difierent cap it is employed. The cap 16 in this case has a smaller vent ii, and extends into the shaft 2 about 1 inches. The vent is in the form of a inch diameter hole inch long at the bottom of the cap, with a inch hole communicating therewith and extending to the top of the cap. At the same time, the circulation through the observation port and the vapor space therein is also restricted by a sleeve which fits snugly into the observation port 5 much as the cap l6 fits into the shaft 2. This sleeve extends approximately to the closest edge of shaft 2, and has a inch hole extending entirely through its center, except for a constriated portion at its lower end. This lower end is blanked 01f except for a inch diameter hole inch in length at its lower side. The flash is observed through this hole, the inch hole communicating ther with extending to the outer end of the sleeve. The outer portion of the sleeve may be enlarged, as is the upper end of cap I6, so as to provide a flange resting against the side of block 1 to hold it in position.

With the cap and sleeve just described, it is apparent that the air circulation within the vapor space is considerably more restricted with the Pensky-Martens equipment than with the Cleveland Open Cup equipment. Not only the vapor space, but the open passages leading to the outside of the block, are considerably smaller.

In duplicating the results of, the conventional Tagliabu Closed Cup flash method, still further restriction in the circulation of air into the vapor space is desirable. In this case, a cap and a sleeve, both similar to the Pensky-Martens cap and sleeve, are employed, except that the cap is solid, i. e. contains no vent ll at all. Under such conditions, results substantially duplicating those of the conventional Tagliabu method are obtained.

In the above examples, it may be calculated that the ratio of the vapor space to the liquid volume is about 16 to 1 for the Cleveland Open Cup and about 2.8 to 1 for the Pensky-lviartens and Tagliabu tests. If apparatus is used which is to accommodate a different liquid volume, approximately the same ratios should be used for the various tests, 1. e., between about 12 to 1 and 20 to l for the Cleveland Open Cup, and between about 1.8 to 1 and 3.5 to 1 for the Pensky-Martens and Tagliabu tests. For example, if equipment is built or used for 0.1 ml. of liquid, the vapor spaces used in the above examples should be reduced to about the sizes described; but the vents described above would be satisfactory without change.

The importance of the various design factors indicated above is well illustrated by the fact that when the Cleveland Open Cup micro method is employed with a difierent cap l6, results which tained. Thus when no cap at all is employed, the

results obtained are 15 F. to 20 F. higher than the macro method results; when a solid cap, i. e.

one having no vent I! but otherwise of the same dimensions indicated above is employed, the results are about 20 lower than the macro method results; when a cap it is employed with a vent I! which is too large, 1. e. A, inch instead of inch as indicated above, results about higher than the macro results are obtained; and when a cap was employed which had a inch vent but extended about A inch deeper into shaft 2, values about lower than those of the macro method were obtained. In the latter case, it will be noted that not only the vapor space to liquid volume ratio changed, but also the length of the vent hole was nearly doubled, increasing the resistance to air flow. Similarly, variations are observed with the Pensky-Martens and Tagliabu methods; but

in all cases it has been found possible to employ the degree of air circulation, and the cap fitting into shaft 2 and the sleeve fitting into port 5, may be considered as means for providing limited air circulation in the vapor space.

Although the apparatus and method have been described in detail in the specific examples above, it is clear that variations may be made which are within the scope of the invention. Thus the equipment may be altered in size so as to accommodate larger or smaller samples as indicated above. In such cases, the results of the corresponding macro method may be substantially duplicated by employing approximately the same ratios of vapor space to sample volume, and approximately the same resistance to air flow as indicated above in the specific examples. This resistance may be altered by changing the length of the passages or their size, in accordance with well known principles of fluid flow, e. g., by use of the Fanning equation to determine the size and length of a passage which will permit the same amount of air to flow therethrough under the same conditions. It is clear also that other forms of liquid receptacle than that shown in the drawing may be used, as long as the receptacle is located in the central portion of the block and is provided with the proper vapor space and vents. It is preferable, however, that this receptacle be shallow, i. e., have a large upperdiameter as compared with its depth, so as to provide a large surface area. The igniter or means for producing an electric spark, may be any conventional means which accomplishes the purpose, as long as the spark so produced is not so hot as to cause excessive vaporization and turbulence and not so bright as to obscure the flash. Preferably it should not extend into the flash chamber as far as indicated in Figure 1. The glass insulation should extend to approximately the edge of shaft 2, and the electrode 8 should be bent downward at the tip of the insulation so as to leave a spark gap of about inch along the underside of the insulation between the electrode 8 and the walls of shaft 2 at the point at which the igniter shaft 6 enters it. This spark will then occur at a distance about inch above the surface of the liquid in receptacle 4.

The unrestricted space above the liquid recep' tacle 4 within shaft 2 is termed the vaporization space or vapor space, although it is apparent that vapors will also accumulate in vent I? and observation port 5. The latter two vents provide passages for circulation of air to and from the vapor space, and port 5 also serves as an observation port, where visual detection of the flash is employed. As previously indicated, the size of the vapor space 3 and the dimensions of the vent passages IT and 5 are chosenso as to duplicate the results of the macro flash methods. The combined vapor space 3 and liquid receptacle space 4 are referred to as the flash chamber.

While a specific shape of flash chamber, and the use of a cap in shaft 2 and a sleeve in port 5 have been described, it is obvious that other shapes of flash chamber and other designs of the block may be employed. Thus the cap and sleeve could be eliminated providing the proper ventilation and some means for detecting the flash are provided for.

Although visual detection of the flash through the observation port 5 is quite satisfactory, particularly since the interior of the block is always dark, so that the flash may be easily observed even in a well lighted room, other methods of flash detection, such as the use of pressureor light-sensitive devices mechanically or electrically operated, may be employed. Similarly a thermocouple or other conventional device may be employed in place of the thermometer [5. Whatever means of measuring the temperature is employed, the temperature should be measured at a point outside of but adjacent to the liquid receptacles, and both the flash chamber and the point of temperature measurement should be located centrally within a block of highly heatconductive material, preferably a metal such as aluminum, copper, brass, silver, steel, or the like. The block may be insulated, if desired, and any means of heating it may be used, such as electricity, steam coils, etc.

It is to be observed that the observation port '5 slopes upwardly. This has been found to be most desirable, not only from the standpoint of ease of observation, but for ease of obtaining reproducible results. The angle with the horizontal also affects the resistance to air flow through the vapor space. It may vary between about 10 and 60, but is preferably about 20 as indicated in the drawing.

Other modifications of the invention which would occur to one skilled in the art are to be included within the scope of the invention as defined in the following claims.

We claim:

1. A device for determining the flash point of inflammable liquids on a micro scale, which comprises a block of highly heat-conductive material so formed as to provide a flash chamber comprising a shallow liquid receptacle centrally located within said block, there being three passages extending from said flash chamber to the outside of said block, the first passage extending upward and the second and third passages extending laterally, a cap adapted to fit into the outer end of said first passage, means insertable through said third passage for producing an electric spark in the vapor space just above the liquid receptacle, means for heating the block at a controlled rate, and means for determining the temperature of the block at a point adjacent to the liquid receptacle.

2. An apparatus for determining the flash point of inflammable liquids, which comprises a metal block having a flash chamber comprising a liquid receptacle located centrally therein, there being a first passage extending upward from the liquid receptacle to the outside of said block and a second passage extending laterally from just above said liquid receptacle to the outside of said block, a cap adapted to fit into the outer end of said first passage, there being a vent hole through said cap permitting a limited circulation of air from outside said block through the vapor space above said liquid receptacle 7 through said passages, means for producing a spark in said flash chamber just above said liquid receptacle, means for heating said block, and means for measuring the temperature of the block at a point adjacent the flash chamber.

3. A device for determining the flash point of inflammable liquids on a micro scale, which comprises a block of highly heat-conductive material so formed as to provide a central flash chamber comprising a shallow liquid receptacle of size suflicient to hold between about 0.1and 1.0 ml. of liquid and a vapor space of at least 1.8 times the volume of said liquid receptacle extending thereabove, said vapor space being formed by a shaft extending upward from said liquid receptacle to the outside of said block and a cap adapted to flt into the outer end of said shaft, and said cap having a vent hole passing therethrough there being an observation port extending from said vapor space just above the liquid receptacle to the outside of the block at an angle between about 10 and 60 above the horizontal; means for producing an electric spark in the vapor space just above the surface of the liquid in the flash chamber, means for heating the block at a controlled rate, and means for determining the temperature of the block at a point adjacent to the flash chamber,

4. A device for determining the flash point block provided with a vertical shaft extending to a central point therein and an observation 7 port extending upwardly at an angle between about 10 and 60 from a point just above the bottom of said vertical shaft to the outside of said block, a cap extending part of the distance into said shaft from the upper end thereof, a vent hole through said cap to provide limited circulation of air from the outside of said blocl: through said vertical shaft and said observation port, means for producing a spark in the lower portion of said shaft, means for heating said block, and means for determining the temperature of the block at a point adjacent to the lower end of said shaft.

5. A device according to claim 4 in which the means for producing a spark comprises an electrode adapted to pass through a third passage leading from the outside of said block to a point just above the bottom of said vertical shaft, said point being located so as to be invisible through said observation port.

References Cited in the file of this patent UNITED STATES PATENTS Yumber Name Date 218,066 Saybolt July 29, 1879 FOREIGN PATENTS Number Country Date 18,076 Germany May 2, 1882 185,814 Great Britain Sept. 4, 1922 620,654 France Jan. 22, 1927 552,706 Germany June 17, 1932 

